Sia POW Storage vs Best Centralized Storagebrowsing

Hi, I'm new to this forum. Was recently aware that Siacoin plans to switch to proof-of-work algorithm and implement in sometime in 2018. Sia has contracted a third party to build it's POW miner. I basically had just two questions and was wondering if someone might have the answers.

First question: If 'quota' of 4000 miners isn't reached for obelisk miner pre-order, how will that affect the number of coins mined at a later date?

Second question and more important to Sia's success: I have a friend who's been using Amazon's "unlimited everything plan". Last month he was charged $18 per 4.5 TB of data retrieval from his storage account which works out to $4 per 1 TB of data. This is almost competitive with Sia's projected storage price of $2 per TB, but now that Sia's decided to implement one of the most inefficient algorithms around (POW), to what extent if any will this affect Sia's projected storage costs of $2 per TB?

It seems like you don't really know how Sia works, since these questions are based off false assumptions or rumors. I'll tackle them one by one.

Was recently aware that Siacoin plans to switch to proof-of-work algorithm and implement in sometime in 2018.

Sia is not going to change its PoW algorithm and probably never will. It has always used Blake2b mining. The news you're probably referring to is the Obelisk ASIC miner, which is a hardware miner that will replace the GPU miners that we have now.

If 'quota' of 4000 miners isn't reached for obelisk miner pre-order, how will that affect the number of coins mined at a later date?

The number of Obelisks sold won't affect coin generation at all. Like any cryptocurrency coins can only be generated by mining blocks, and speed is limited by the time between blocks. If blocks take less than 10 minutes to generate the diff increases, if they take longer than 10 minutes it decreases, that way it should always stay around 10 minutes. In the end Obelisks will only increase the difficulty.

This is almost competitive with Sia's projected storage price of $2 per TB, but now that Sia's decided to implement one of the most inefficient algorithms around (POW), to what extent if any will this affect Sia's projected storage costs of $2 per TB?

The cost of storage is completely decided by the asking price of the hosts on the network, has nothing to do at all with mining coins.

I suggest you take a look at some documentation on the wiki (https://siawiki.tech) so you can learn about how Sia really works.